Determination of heavy metals in soil by
atomic absorption spectrometry(AAS) Name: XuFei Group: The 3rd group
Date: Sep. 20th 2012
Part 1 The introduction
1.1The purposes
(1)Learn how to operate the atomic absorption spectrometry;
(2)Learn how to do the pretreatment of soil samples;
(3)Get familiar with the application of atomic absorption spectrometry.
1.2The principles
Atomic Absorption Spectrometry (AAS) is a technique for measuring quantities of chemical elements present in environmental samples by measuring the absorbed radiation by the chemical element of interest. This is done by reading the spectra produced when the sample is excited by radiation. The atoms absorb ultraviolet or visible light and make transitions to higher energy levels .
Atomic absorption methods measure the amount of energy in the form of photons of light that are absorbed by the sample. A detector measures the wavelengths of light transmitted by the sample, and compares them to the wavelengths which originally passed through the sample. A signal processor then integrates the changes in wavelength absorbed, which appear in the readout as peaks of energy absorption at discrete wavelengths. The energy required for an electron to leave an atom is known as ionization energy and is specific to each chemical element. When an electron moves from one energy level to another within the atom, a photon is emitted with energy E. Atoms of an element emit a characteristic spectral line. Every atom has its own distinct pattern of wavelengths at which it will absorb energy, due to the unique configuration of electrons in its outer shell. This enables the qualitative analysis of a sample.
The concentration is calculated based on the Beer-Lambert law. Absorbance is directly proportional to the concentration of the analyte absorbed for the existing set of conditions. The concentration is usually determined from a calibration curve, obtained using standards of known concentration. Calibration Curve Method: Prepare standard solutions of at least three different concentrations, measure the absorbance of these standard solutions, and prepare a calibration curve from the values obtained. Then measure the absorbance of the test solution adjusted in concentration to a measurable range, and determine the concentration of the element from the calibration curve.
Part 2 The materials and apparatus Atomic absorption spectrometry; Cu hollow cathode lamp; AC voltage stabilizer; oil-free gas compressor; acetylene cylinder; oscillator; sample boat; Erlenmeyer flask with stopper (100 ml); beaker; graduate cylinder; pipette.
Part 3 The procedure
3.1 operating procedure for AAS
(1) inspect major components to ensure operating normal.
(2) Install required hollow cathode lamp. Sele ct “T” before turning to the power and hollow cathode lamp. Then select appropriate la mp current and preheat for 30min.
(3) Make sure electrical meter to point to zero and then turn on high-voltage power.
(4) Select appropriate slit width.
(5) Rotate monochromator and select required wavelength. If the power meter is too high or low, adjust negative high voltage until the meter reads full scale.
(6) Adjust light point and wavelength so that the meter represents the maximum value.
(7) Turn on air compressor and acetylene gas and ignite flame. Adjust the flame appropriately and preheat the burner.
(8) Inject distilled water into the flame and continue to preheat the burner. Inject distilled water into the flame after each sample.
(9) Select “E”, inject blank solution into the flame and adjust the meter to zero.
(10) Optimize analysis conditions and measure standard solution and samples.
(11) After completion of measurement, turn off acetylene gas valve and then air compressor, cut off gas supply a moment later.
(12) Select “T” before turning o ff high voltage power, decrease lamp current and then turn off the lamp. At the same time, all buttons should be on original positions. (13) Check the equipment before leaving the laboratory.
3.2 Determination of soil samples
(1) Preparation of extracting solution (0.05 mol/l EDTA solution)
18.6 g of EDTA is dissolved with water in a beaker (500 ml). The PH is adjusted to 7.0 using dilute ammonia. The mixture is transferred into a volumetric flask (1000ml), dilute to the mark and mixed well.
(2) Treatment of soil samples
2.50 g of air-dried soil (60- 100 mesh) is put into an Erlenmeyer flask with stopper (100 ml). 12.5 ml of EDTA solution is added. The mixture is shaken for 1h and then filtered. The filtrate is preserved for analysis.
(3) Preparation of Cu standard stock solution
0.10 g of Cu is dissolved in 15 ml of (1:1) nitric acid solution. The mixture is transferred into a volumetric flask (1000 ml) and diluted to the mark with re-distilled water. The concentration of the stock standard solution is 100g/ml. (The concentration should be calculated according to the mass of Cu).The working Cu standard solution (10µg/ml) is obtained by diluting 10 ml of Cu standard stock solution to 100 ml with
re-distilled water.
(4) Plotting of the standard curve
0 ml, 1 ml, 2 ml, 3 ml, 4 ml and 5 ml of Cu standard solution (10µg/ml) are added respectively to 6 volumetric flask (10 ml) with 1 ml of 5 mol/l hydrochloric acid. The mixture is diluted with re-distilled water and mixed well to give 0µg/ml, 1.00µg/ml,2.00µg/ml, 3.00µg/ml, 4.00µg/ml, 5.00µg/ml of Cu, respectively. The absorbance is measured at wavelengths of 3247 Å. The standard curve is constructed by plotting absorbance vs. concentration.
(5) Determination of samples
The sample solution is analyzed using the same procedure and conditions as for the standard curve. The concentration of Cu is obtained from the standard curve based on the absorbance.
Part 4 The results
4.1 The raw data
4.2 AAS standard curve
4.3 Calculation
The absorbance of sample is 0.0511.
According to the formula above :y=0.0446x+0.0024,R2=0.9997
The concentration of Cu in the sample is:1.091mg/L.
Part 5 Discussion
In this experiment, we use the AAS to determine Cu in soil. I learn how to operate the AAS and the limitation. In the experimental process, standard solution was prepared in strict accordance with the experimental requirements and I learn how to deal with the data. Finally we get the standard curve, then, the sample concentration is calculated according to the absorbance of the sample.
In the experiment we have nine members in our group, so we can do our best in every work we need to do. For my work,I am responsible for the preparation of solution and titration. What’s more, I learn how to use and operate the AAS on the computer later.
Ultimately, we get the linear formula is y = 0.0446x + 0.0024 and R2=0.9997. From According to the formula and the absorbance of Cu in the sample is 0.0511, we draw the concentration of Cu in the sample is 1.091µg/ml. We have known that the concentration of test sample measured by instrument is 1.091mg/L.
We can say our result of experiment is so very accurate from the standard curve of Cu and the value of R(R2=0.09997). The accurate data is due to the efforts of we everyone. Thanks for every members of our group.
I have some suggestions for our experiments. Firstly w hen we’ll do an experiment, we must prepare our pre-lab by ourselves and translate it into Chinese .Only do like this, we can understand the experiment well. Secondly we should prefer to solute the problems in the experiment rather than ask for TA. Finally, everyone should understand his own task in the experiment.
Ruby Tan Partner: Kathryn Zhu 04/19/12 LAB#24SL:Musical Intervals Objective: To determine the frequency ratios for common musical intervals. Procedure: Come into the lab, open DataStudio, switch on the interface, select Create Experiment, then Sound Creator. Change simultaneous tones to 2. Then put on the headphone to listen the voice, changing the wave of a sound to a longer wave(lower tones). Hum the indicated for a specified interval and find the pitch for the 2nd note. Do it for 5 times with 5 different songs. Ruby Tan Partner: Kathryn Zhu 09/29/11 LAB#24SL:Musical Intervals Conclusion In this lab, we know the wave of the songs concern with the tones of it. Shorter period waves have a lower tones. Amplitude cause the loudness of the songs. This lab is good for us to analyze the notes of all the songs.
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Title The title for the lab report may be provided by your lecturer. If not, you will need to make up your title. It should be brief, informative, and interesting. It is not usually a sentence. You should aim to provide just enough information in the title to avoid it being overly general. The key is to be concise and meaningful. Check with your lecturer if you need to include a title page and ensure all the relevant information is supplied. This will include your name, student number, date of the experime nt, the demonstrator’s name and the group you belong to. Introduction The introduction should be clear and concise. It should tell the reader what to expect in the report. An introduction generally includes the following elements: ? Problem – State the issue investigated by the experiment. ?Background –Briefly summarise previous research on the topic and narrow the scope of the study. ? Objectives – State the aim of the experiment and state the methods used. ? Hypothesis – If this is not already given, you must formulate this in unambiguous terms. The introduction is written in the past tense following the scientific style of writing. Materials and methods This section should contain a clear enough explanation of how you conducted the experiment so that someone wishing to replicate the procedure may be able to do so. Here you should describe the experimental design, the treatments and the apparatus you used. You should follow the rules for the conventional descriptions of chemicals. The standard practice is not to use trade names for chemicals. Instead you should use the generic or chemical names. Standard apparatus should be described in proper technical terms. Also, you should describe the procedures and methods of measurement you used. At the end of this section you should provide details of how you analysed the data. If this involved lengthy statistical calculations, these should be attached as an appendix. Results and discussion This section should be organised in a systematic way such that you first present the results and then discuss them. To report on results you should describe what happened. This is perhaps the most important section of your report because it is where you report the data upon which your conclusions are based. Accuracy, clarity of expression and systematic presentation of the data (e.g., use of tables, graphs, figures, diagrams, etc.) are key factors here. Take note that tables and figures do not simply repeat information given in the text –they are meant to summarise, amplify, or complement it. You should report first the results that bear directly on the title of your lab report. Any other interesting findings should follow this. If the experiment had more than one hypothesis, you may want to organise your results in a way that reflects this. A key
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Metal Tensile Test 1.The purpose: ①Measure the yield limit, the ultimate strength, the elongation fracture of low carbon steel. ②Measure the ultimate strength of cast-iron. ③Observe the phenomena when low carbon steel and cast-iron are pulling, work out the curve that the deformation changing with the outer force(F-△L curve). 2. The equipments and the instruments. Universal material testing machine, screw micrometer. 3. Sample. In this experiment, we choose “ten times sample”, which means L o=10d o. 4.The theory in this experiment. ①The experiment of pulling low carbon steel. There are 4 stages in the deformation of low carbon steel: elastic stage, yield stage, intensive stage, local deformation stage. P s is the minimum load in the second stage. And P b is the load after which the sample comes to the 4th stage. ②The experiment of pulling cast-iron. There is no yield stage in the test of cast-iron, when the load comes to the ultimate strength P b, cast-iron will broken. And
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科学实验报告英文写作稿纸(四线三 格)(A4直接打印).txt 科学实验报告英文写作稿纸(四线三 格)(A4直接打印) n In this scientific experiment。___ [___ ___]。___ and analyze the results to support or reject the ___. ___ Materials List the materials and ___] Methods 1.[Explain the step-by-step re followed during the experiment] 2.[___ made to the standard re] Results
Present the ___ appropriate charts。tables。or graphs to visualize the data collected] n 1.___. 2.Discuss ___ or errors that may have occurred during the experiment. https://www.doczj.com/doc/d619169942.html,pare and contrast the results with existing ___ on the same topic. n Summarize the main findings of the study and their ___.] ___ Cite any sources used for background n or to support the n of results] Appendix Include any supplementary n or nal data。if applicable]